He is likely to face this tough question: Why did you make Apple devices so easy for criminals and terrorists to use? Cook, of course, will have a good answer to that. But the question goes to heart of the debate over domestic surveillance, consumer privacy, and national security.

In recent months, Apple and other tech companies have hardened their stance on encryption, introducing "strong" encryption by default that cannot be decrypted even when law enforcement has a warrant. It's great for the privacy of consumers, which has been abused by government agencies like the NSA who have spent years spying on their own citizens.

But it's bad if you're a security agency trying to catch terrorists or other dangerous criminals. There is just no way for law enforcement to read soemthing if it's properly encrypted — which lets the bad guys as well as the good guys comunicate in secret. One senior American police officer said that the iPhone will become the "phone of choice for the paedophile."

It's easy to understand law enforcement's frustration. As products using strong encryption become more widespread, they're losing access to sources of information they once had. It's making their jobs considerably harder. But on the other hand, encryption proponents argue that by introducing back doors for the government, it weakens the entire system and puts potentially sensitive data at risk. "There is no back door that only works for good guys," says author and activist Cory Doctorow.

As such, Cook's comments at the White House summit, which is to be held at Stanford University, will be closely monitored.

In an open letter on Apple's website, Cook previously wrote that the company has "never worked with any government agency from any country to create a backdoor in any of our products or services. We have also never allowed access to our servers. And we never will."

And in the wake of the leak of dozens of high-profile female celebrities' intimate photos last year, Cook also addressed the issue on an interview with Charlie Rose. (It's believed the files were stolen from Apple's iCloud cloud hosting service.) "Things [were] written in the press that people had backdoors to our servers," he said. "None of that is true. Zero. We would never allow that to happen. They would have to cart us out in a box before we would do that."